Bicycles are widely used for transportation and recreation. A typical bicycle includes a rear wheel carried by a frame and a front wheel carried by a fork which, in turn, is rotatably connected to a forward portion of the frame. In particular, a steering tube is connected at its lower end to the fork and extends through a corresponding passageway defined in the forward portion of the frame. An upper portion of the steering tube is connected to a bicycle stem.
The bicycle stem includes a steering tube clamping portion which clamps to the upper end of the steering tube. A body portion extends generally forwardly and at an upward incline from the steering tube clamping portion and terminates at a handlebar clamping portion. The incline is generally upward for mountain biking and downward for road biking, as desired by the rider. Of course, the medial portion of the handlebar is connected to the handlebar clamping portion of the stem. The rider is thus able to steer the front wheel by turning the handlebar.
The stem is important for proper orientation and positioning of the rider relative to the bicycle. In addition, the stem is desirably relatively strong to avoid potentially catastrophic failure, and is also desirably lightweight to reduce the burden on the rider. Mountain or off-road biking can put especially high demands on the strength of the stem. Road bikes may also place high demands in terms of both required strength and being relatively lightweight on the bicycle stem.
The stem also desirably has relatively high torsional stiffness, that is, a resistance to allowing the handlebar to rotate as the rider pushes on one side while lifting on the other. If the torsional stiffness is too low, the rider's energy is more quickly and wastefully depleted in rotating the handlebar.
A widely used type of bicycle stem includes a body portion or tube and a steering tube clamp connected to an end of the body tube. The steering tube clamp is in the form of a split tube with a vertical slot opposite the body tube. One or typically two bolts or other fasteners are used to secure clamp together at the vertical slot. Unfortunately, the clamp and fasteners extend backward toward the rider and may present an object which the rider may strike or bang with his knees, for example, such as during vigorous riding.
Another type of steering tube clamping arrangement attempts to remove the clamp and bolts from protruding backward into the rider's space. This type of stem includes a vertically oriented tubular portion defining a main passageway that receives the upper end of the steering tube. To secure the stem relative to the steering tube a clamp may be positioned within a second passageway that extends transverse to the main passageway and which is in communication with the main passageway. The clamp typically includes two cylindrical halves or clamping members which can be urged together by a single fastener, such as a bolt which extends along an axis defined by the cylindrical halves. More particularly, the cylindrical halves each include corresponding arcuate recesses which when properly aligned will press against an outer circumferential portion of the steering tube upon tightening of the bolt to thus clamp the bicycle stem to the steering tube. Such stems are shown, for example, in U.S. Pat. Nos. 5,687,616 and 5,842,385.
Unfortunately, the transverse clamp for the steering tube has relatively little surface area to contact the steering tube. The outermost ends may define contact points which bite into the steering tube, thus forming dimples in the metal steering tube. Such deformations of the metal steering tube may be undesirable for a number of reasons. For example, the dimples may subsequent fine adjustment, since the clamp will tend to seat into the dimples. In addition, for a composite material steering tube an entirely different type of clamping arrangement may be needed to avoid causing damage in the composite material which may propagate to failure of the steering tube. Such composite steering tubes are often used on high-end road bicycles, for example.
Yet another difficulty or shortcoming of many conventional bicycle stems is that have a recess of uniform diameter to grasp or clamp to the handlebar. This uniform diameter may be sufficient for a handlebar with a corresponding uniform diameter at the clamping area; however, many handlebars include a slight bulge or enlarged diameter portion at the clamping area. Accordingly, a conventional clamp will permit the handlebar to wobble slightly. In addition, the clamp will experience greater stress since it is only tightly contacting the handlebar at interior portions of the recess. These shortcomings may lead to failure of the handlebar clamping portion, or unacceptable wobble or loosening of the connection to the handlebar.